1. Field of the Invention
The present invention relates to a method and a device for controlling a board stopping position in a board transfer device provided in, such as, an electronic component mounting machine or the like wherein a board is stopped at a target position on a transfer pathway.
2. Discussion of the Related Art
As equipment for manufacturing a board on which various kinds of electronic components are mounted, a cream solder printing device, electronic component mounting machine, a reflow soldering device and inspection device are used for manufacturing and in many cases, these devices and machines are operatively connected with one another by a board transfer device thereby to structure a board production line. Among these devices, the electronic component mounting machine is structured mainly by a board transfer device for bringing in and stopping a board at a position where the components are to be mounted, a component supply device for supplying electronic components and a component mounting device for mounting the electronic component to a predetermined position on the board. It may be difficult for a single mounting machine to mount all of the desired different kinds of electronic components and accordingly, the electronic component mounting line is sometimes formed by arranging a plurality of modularized mounting machines in-series.
It is popular for a board transfer device used for a board production line or an electronic component mounting line to transfer the board placed on a conveyer which forms the transfer route or pathway. Further, as one of the controlling methods for stopping the board at the target position, there has been introduced a method in which the board is transferred further by a predetermined distance when a board sensor provided at a position of the transfer pathway detects a board end portion. According to this method for controlling the board stopping position, when an electronic component is mounted on the board extending beyond the end portion of the board and the entire length of the board with the component mounted thereon becomes elongated, stopping the board at the target position becomes difficult due to possible erroneous detection of the sensor. For example, when a connector part is mounted on the board with a portion extending beyond the front end portion of the board, the board sensor detects the front end portion of the connector part, which may lead to an occurrence of detection error by the value of extended length of the connector part. Then the board is stopped before the target position by the extended length and detecting of correct stopping position becomes difficult. This will lead to occurrence of difficulties in reading a reference mark on the board and/or difficulties in mounting electronic components by the component mounting device.
An example of the technology for maintaining and improving accuracy of stopping position controlling by detecting an end portion of the board has been introduced in JP2003-31991 A in which a method and a device for detecting a circuit board for a circuit board production device are disclosed. The circuit board detecting method according to JP2003-31991 A is performed by utilizing a first board detecting sensor for detecting a reflected light reflected from a board by irradiating the board with diffusion light and a second board detecting sensor for detecting a reflection light reflected from the board by irradiating the board with converging light, wherein one of the first and the second sensors is selectively applied depending on the type of the circuit board. Thus, even a plurality of boards with perforation or recess or a circuit board with various electronic components already mounted thereon can be accurately detected with high reliability.
The method disclosed in JP2003-31991 A improves the detection accuracy by selectively applying the diffusion light and the converging light depending on the type of board. Erroneous detection of the end portion of the board can be prevented by the fact that the converging light passes through the perforation or the recess and is not reflected or the fact that an amount of reflected light varies depending on the surface condition of the electronic component already mounted on the board. However, this method cannot overcome the detection error occurrence, which may be derived from the mounting of the electronic component which extends beyond the end portion of the board. It would be still difficult to accurately detect the original end portion of the board by a mere selection of diffusion light and the converging light considering that type of the component extended from the board, the amount of extension (extended length) or the extended width varies depending on the board type to be produced. Accordingly, it would be difficult to accurately stop the board at the target position on the transfer pathway.
Further, according to the method of JP2003-31991 A, a plurality of sensors are necessary to be equipped and a selection control device therefor is also necessary, and accordingly there is a problem that the production cost becomes high.